Well, it depends - you've given us a word without context, so we cannot say for sure.
If it is a part of verb, as in was screaming, then it would be a participle, or a verb.
But if it is next to a noun, for example, a screaming disaster, then it would be an adjective.
It can also be a noun sometimes, as in Screaming is always fun.
The only thing it cannot be is adverb.
